The long-tern objectives for this project are to identify, and map both genetically and physically, those genetic elements and regions which are involved in the synthesis, structure/function, and regulation of the inducible intracellular membrane system in teh faculative photoheterotroph, Rhodobacter sphaeroids. This molecular genetic approach, coupled with a detailed biochemical analysis of membrane structure and function will lead to a better understanding of the genetic basis for membrane synthesis and regulation. The importance of biological membranes to normal cellular activities is best reflected in the alterations of such membranes in the neoplastic state, or the properties of altered membranes in myotonia, or the alteration in intestinal hexose transport in familial glucose-galactose malabsorption, to mention a few. As additional long-term objectives, we propose to examine: the origins of anoxygenic photosynthesis, the development of the diploid state and the evolution of the mitochondrial line of development. These long-term objectives will be specifically addressed through the isolation, identification, complementation and mapping of genes directly involved in intracellular membrane synthesis and regulation with special emphasis directed towards the early steps in porphyrin ring biosynthesis as well as the development of unique enrichment/selection conditions for the isolation of novel mutant strains defective in membrane synthesis and/or regulation. Because of high quanine plus cytosine content (70%) of R. sphaeroides particular attention needs to be directed to the expression of these genetic elements as well as the development of genetic or pseudogenetic systems which will facilitate a detailed analysis of these complex processes. In addition, the presence of two distinct chromosomes in R. sphaeroides representing for a number of genetic loci, a merodiploid state, represents a unique opportunity to investigate the interaction between separate linkage groups in this very primitive experimental system. In particular, the maintenance of the physical structure of each linkage group, its genetic stability and the interaction of each linkage group at the level of gene expression shoul further our understanding of the origins of more complex systems. Our ability to employ a relatively simple genetic system as a tool to better understand the more complex interactions between homologous as well as non-homologous chromosomes can lead to a fuller understanding of the diploid state in eukaryotic systems.